Dream Yacht Charters (DYC) is the largest charter company by any measurement. With bases all over the world and a very wide variety of monohulls and catamarans, the options are nearly endless. DYC feels a bit more like a "franchise" model with many of their locations operating like affiliates vs. fully owned and operated by the parent company. This allows them to expand quickly but does pose some risk as each base experience can vary.
DYC also provides the most charter options of any charter company. You can rent a cabin for a week or take a boat across the Atlantic for a 6 month sabbatical.
DYC's ownership options are also vast including the common "guaranteed income" and "performance based" options but also including unique offerings like their "Fractional Ownership" program.
If you're planning to charter, DYC will almost certainly be an option.